Func<Customer, Boolean> f = DynamicLinq.ParseToFunction<Customer, Boolean>("Name == 'Gian Maria'");
Assert.That(f(aCustomer), Is.True);

This example shows that I can build a simple function that accepts an entity (Customer) and a string representing some conditions, then I’m able to dynamically parse the string, create an expression tree and call Compile on it to obtain a function that I can use in code. As soon as possible I’ll show a complete example if you are interested in.

alk.

Tags: LINQ Dynamic Expression Generation

The user can Add and Remove element from the navigator, or directly from a DataGridView, and I simply need to call the appropriate method of Repository to save and delete objects. This structure is really clean, but you encounter a problem: nor the BindingSource nor the BindingList<T> raises a RemovingItem event. I do not know why these classes are designed in this way, you have an AddingNew Event in the Binding Source and BindingList<T> but no corresponding RemovingItem. You have a ListChanged event that tells you when an element is removed, but the element is already gone from the list, so you cannot use to detect object removal.

If you look at the events of BindingList<T> you can notice that there is no way to be informed of the exact element that gets removed. A simple solution is to inherit from the BindingList<T>

public class RemoveItemEventArgs : EventArgs
{
    public Object RemovedItem
    {
        get { return removedItem;}
    }
    private Object removedItem;

    public RemoveItemEventArgs(object removedItem)
    {
        this.removedItem = removedItem;
    }
}

public class MyBindingList<T> : BindingList<T>
{
    public event EventHandler<RemoveItemEventArgs> RemovingItem;
    protected virtual void OnRemovingItem(RemoveItemEventArgs args)
    {
        EventHandler<RemoveItemEventArgs> temp = RemovingItem;
        if (temp != null)
        {
            temp(this, args);
        }
    }

    protected override void RemoveItem(int index)
    {
        OnRemovingItem(new RemoveItemEventArgs(this[index]));
        base.RemoveItem(index);
    }

    public MyBindingList(IList<T> list) : base(list)
    {
    }

    public MyBindingList()
    {
    }
}

As you can see implementing such a functionality is a breeze, you should simply override the RemoveItem method and raise a custom RemovingItem event. Now I can use this new BindingList in this way.

MyBindingList<UIDomainProxy> source = new MyBindingList<UIDomainProxy>(
    Repository<Domain>.GetAll().Select(d => new UIDomainProxy(d)).ToList());
source.AddingNew +=source_AddingNew;
source.RemovingItem +=source_RemovingItem;
domainBindingSource.DataSource = source;

I gets all the element from the repository, then I wrap then in a UIProxy (I’ll explain this in a future post), then I intercept the addingNew and RemovingItem events simply calling Save and Delete methods from the repository. Finally I set the BindingList as the source of the BindingSource created by the designer.

I wonder why this event is missing from the basic BindingList<T> implementation.

alk.

Tags: " rel=tag>BindingList .NET Binding Windows Forms

Here is the content of the storage file

<?xml version="1.0" encoding="utf-8"?>
<Comments>
  <Comment>
    <Author>Hacker</Author>
    <CommentText><![CDATA[you where <script>alert('hacked');</script>]]></CommentText>
  </Comment>
</Comments>

In Default2.Aspx there is a simple solution to mitigate this problem, trying to remove all node that are not <b>, but with this solution if a user enter “this is a <b>good comment</b> with <i>italic text</i>“, we have a big problem, the part in the <i></i> tag gets completely removed. Moreover if some hacker gets a way to change your storage file, or can insert some data in database you still have problem. A better solution was showed in Default3.aspx. Since I consider data in the file as untrusted input because it is under direct control of the user I need to sanitize the comment before I can render text to the user. The goal is having a SanitizeComment function that gets a html fragment as input and return a new fragment with all tags removed, except those that are permitted.

 1 private String SanitizeComment(String commentText)
 2 {
 3   try
 4   {
 5       XElement doc = XElement.Parse("<span>" + commentText + "</span>");
 6       doc.Descendants().Where(elem => elem.Name != "b")
 7          .ToList().ForEach(elem =>
 8          {
 9              elem.AddAfterSelf(new XText((String)elem));
10              elem.Remove();
11          });
12 
13       String retvalue = doc.ToString();
14       return retvalue;
15   }
16   catch (System.Xml.XmlException)
17   {
18       return AntiXss.HtmlEncode(commentText);
19   }
20 }

This code use Linq2Xml; first of all in line 5 I create a XElement with a concatenation of a <span> tag and the original content of the comment. Then I select in line 6 all the XML nodes that have a name different from “b”,(the only permitted tag in the output). Then for each of the unpermitted nodes I simply add a new XML node of type XText after the node, and then remove the original node.

If some XMLException occurs, it means that the input is not a well formed XML fragment, so I default to use the AntiXss HtmlEncode function that avoid any cross site scripting risk.

Here is a result of the page when the storage file contains this comments.

<?xml version="1.0" encoding="utf-8"?>
<Comments>
  <Comment>
    <Author>Hacker</Author>
    <CommentText><![CDATA[you where <script>alert('hacked');</script>]]></CommentText>
  </Comment>
  <Comment>
    <Author></Author>
    <CommentText><![CDATA[this is a <b>good comment</b>]]></CommentText>
  </Comment>
  <Comment>
    <Author></Author>
    <CommentText><![CDATA[this is a <b>good comment</b> with <i>italic text</i> and <b>again Bold<i> italicbold</i></b>]]></CommentText>
  </Comment>
</Comments>

You can see that the content of the file contains dangerous html code, but here is what is rendered by Default3.aspx that calls SanitizeComment function.

As you can notice the alert(‘hacked’) was shown without the <script> tag, moreover all the text between <i> and </i> gets no removed. SanitizeComment function leaves only the tag <b> and remove all other unwanted tags.

sample code here.

alk.

Tags: Linq2XML Security Validation

This is a simple structure where a LogGroup have a collection of LogMessages and each LogMessage has a collection of StackSteps. I have a collection of LogGroup and I need to create a three level master detail interface to make the user browse through all objects in hierarchy.

Thanks to powerful WPF binding you can create such an interface without procedural code. I used three ListView enclosed in a StackPanel. The first peculiarity of WPF binding is that you can set an ObservableCollection<LogGroup> object into the BindingContext on the StackPanel that contains the three listviews . The first listview have this declaration.

<ListView x:Name="GroupsView" ItemsSource="{Binding}"
         IsSynchronizedWithCurrentItem="True"
         HorizontalContentAlignment="Stretch"
         ScrollViewer.HorizontalScrollBarVisibility="Disabled">

The IsSynchronizedWithCurrentItem is true to enable automatic synchronization, the binding is set with the instruction {Binding}, that means “create a binding object with default properties”. A default binding walks controls stack and bind to the first Datacontext property that is not null, in our situation the ObservableCollection<LogGroup> set in the StackPanel that contains the ListView.

Now the second ListView should bind to the property Messages of the item currently selected in the previous ListView, the solution is really simple

<ListView x:Name="GroupsView" ItemsSource="{Binding Path=Messages}"
     HorizontalContentAlignment="Stretch"
     ScrollViewer.HorizontalScrollBarVisibility="Disabled"
     IsSynchronizedWithCurrentItem="true">

The binding is {Binding Path=Messages} that means, “build a Binding object and set the Path Property to the value Messages”, since the IsSynchronizedWithCurrentItem is true you get this master detail binding for free. Thus when you change selection of the first ListView the second ListView updates accordingly and shows the element of the Messages collection of selected LogGroup. To bind the third and last ListView I have to use a special syntax of WPF Path binding

<ListView x:Name="GroupsView" ItemsSource="{Binding Path=Messages/StackSteps}"
     HorizontalContentAlignment="Stretch"
     ScrollViewer.HorizontalScrollBarVisibility="Disabled"
     IsSynchronizedWithCurrentItem="true">

the binding now is {Binding Path=Messages/StackSteps}. If you wonder why I had not written the path “Messages.StackSteps” take a look back at the object model. Messages is a collection, if you write Messages.StackSteps WPF binding engine throws and errors. Now you need to be aware that every exception that is thrown during binding operation is swallowed by the binding engine, and you should look into the debug windows of visual studio to see binding errors. In fact you can find this error

System.Windows.Data Error: 39 : BindingExpression path error: ‘StackSteps’ property not found on ‘object’ ”List`1′ (HashCode=58377472)’. BindingExpression:Path=Messages.StackSteps; DataItem=’ObservableCollection`1′ (HashCode=7457061); target element is ‘ListView’ (Name=’GroupsView’); target property is ‘ItemsSource’ (type ‘IEnumerable’)

the binding engine told you that he could not find a StackSteps Property in the object List<Messages>. In such a situation the WPF binding engine permits you to use slash “/” character to indicate “The current selected item in the view” (read here for more details).  Thus writing the path “Messages/StackSteps” told the engine to take selected LogGroup from the first level, then take the Messages property, then the slash indicates to take the current selected element of Messages collection and finally bind to the StackSteps collection of that element.

Whoa, you get three level master detail with not a single line of procedural code

alk.

Tags: WPF Master Detail Binding Binding

<ListView x:Name="GroupsView" ItemsSource="{Binding}" >
    <ListView.ItemTemplate>
        <DataTemplate>
            <StackPanel Orientation="Horizontal">
                <TextBlock  TextWrapping="Wrap" Margin="2,0,2,0" Text="{Binding Path=LogIdentifier}" VerticalAlignment="Center"  FontSize="14"  />
                <TextBlock Margin="2,0,2,0" Text="Count:" FontWeight="Bold" VerticalAlignment="Center" FontSize="14" />
                <TextBlock Margin="2,0,2,0" Text="{Binding Path=Messages.Count}" VerticalAlignment="Center"  FontSize="14" />
            </StackPanel>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

It is a simple list and each element is composed by three textblock, the first should be the long one and I want it to wrap when the form is resized, the other two are small and should stay to the right. When I launched the form the result is not the desidered one, the first text does not wrap , nor the Count: is aligned to the right. The first error is that you should use DockPanel when you want elements to stay somewhere (right in this situation) and you want one of the element to fill remaining space, then I moved to this solution.

<ListView x:Name="GroupsView" ItemsSource="{Binding}" >
    <ListView.ItemTemplate>
        <DataTemplate>
            <DockPanel >
                <TextBlock  TextWrapping="Wrap" Margin="2,0,2,0" Text="{Binding Path=LogIdentifier}" VerticalAlignment="Center"  FontSize="14"  />
                <TextBlock DockPanel.Dock="Right" Margin="2,0,2,0" Text="Count:" FontWeight="Bold" VerticalAlignment="Center" FontSize="14" />
                <TextBlock DockPanel.Dock="Right" Margin="2,0,2,0" Text="{Binding Path=Messages.Count}" VerticalAlignment="Center"  FontSize="14" />
            </DockPanel>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

You can be still surprised that the result is not the desidered one, the first textblock does not gets wrapped, and “count: X” text is still not aligned to the right. To understand why the layout is arranged in such a way you should consider how the various container constrain dimension for their content. In this post you can find a good description. We have to face two problems, the first is that we want the content of our ListView to have X size equal to that of the listview itself, this can be accomplished with HorizontalContentAlignment="Stretch" attribute, that instructs the ListView to stretch the X size of its content on the horizontal size of the list itself. Then you should instruct the ListView not to show horizontal scrollbar. When scrollbar are enabled the listview grabs the “desidered size” of the controls, then it renders scrollbars accordingly, thus avoiding the word wrapping. To disable scrollbar you can simply use the attribute ScrollViewer.HorizontalScrollBarVisibility="Disabled". Finally you should notice that the order of the elements in the DockPanel is wrong. The dockPanel starts aligning from the first control to the last, and if the last has no DockPanel.Dock specified it is considered to fill remaining space. I need to work from right to left, first element is the number of count, then the Count: string, both with right alignment, finally the text that I wanted to wrap with no Dock specified.

<ListView x:Name="GroupsView" ItemsSource="{Binding}"
         HorizontalContentAlignment="Stretch"
         ScrollViewer.HorizontalScrollBarVisibility="Disabled">
    <ListView.ItemTemplate>
        <DataTemplate>
            <DockPanel >
                <TextBlock DockPanel.Dock="Right" Margin="2,0,2,0" Text="{Binding Path=Messages.Count}" VerticalAlignment="Center" HorizontalAlignment="Right"  FontSize="14" />
                <TextBlock DockPanel.Dock="Right" Margin="2,0,2,0" Text="Count:" FontWeight="Bold" VerticalAlignment="Center" HorizontalAlignment="Right" FontSize="14" />
                <TextBlock TextWrapping="WrapWithOverflow" Margin="2,0,2,0" Text="{Binding Path=LogIdentifier}" VerticalAlignment="Center"  FontSize="14"  />
            </DockPanel>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

Finally I got what I wanted.

I’m doing this post because this morning I woke up early, and wrote again the same wrong XAML (errare umanum est …), when I launch the application I though “mmm I solved this long time ago…” and begin crawling in my projects, then I preferred to do a post, so the next time I can search in my blog.

Alk.

Tags: WPF .NET Framework

With my new 500GB usb disk now I have enough space to work with the virtual machine of the Visual Studio 2010 CTP

alk.

E:\Codice Libri\WCF Unleashed\Examples\Windows Communication Foundation Unleashed
\ef_Chapter5_and_6_WindowsWorkflowFoundation\WCFUnleashedSamples\Chapter 6\Basic
WCFHostedWorkflow\BasicWCFHostedWorkflow\bin\Debug\Interfaces.pdb
Insufficient memory

whoa…it is the first time that xcopy gives me an insufficient memory…

alk.

log1.Debug("TEST");
if (log1.IsDebugEnabled) log1.Debug("TEST");

Boolean isDebugEnabled = log1.IsDebugEnabled;
if (isDebugEnabled) log1.Debug("TEST");

The first version rely on the fact that log4net infrastructure internally checks if debug is enabled so you can call Debug function directly. The second technique is to check if log1.IsDebugEnabled before calling log1.Debug(), and the third stores the IsDebugEnabled in a local variable to check that variable instead of calling IsDebugEnabled each time. If you do one million log calls you will obtain these rough measurements in milliseconds.

log1.Debug("TEST") = 828.125
if (log1.IsDebugEnabled) log1.Debug("TEST") = 750
if (isDebugEnabled)  log1.Debug("TEST") = 31.25

Thus solution 1 and 2 are quite similar in performances, while the third version is obviously the winner because it has not to call the log1.IsDebugEnabled at each run.

Now suppose that the messages is not a constant string but it has to be build

for (Int32 I = 0; I < iterations; ++I)
{
    log1.Debug("TEST" + I.ToString() + "other");
}

In this situation the first test is important

log1.Debug("TEST" + I.ToString() + "other") = 2968.75
if (log1.IsDebugEnabled) log1.Debug("TEST" + I.ToString() + "other") = 75
if (isDebugEnabled)  log1.Debug("TEST" + I.ToString() + "other") = 31.25

The second and third results have the same timing as before, the log is disabled so both conditions evaluates to false as before. The important fact is that the first technique is much more slower, this because even if the debug level is not enable, you have to pay the time to do string concatenation to create the message to send to log.Debug function.

The conclusion is: always check if the log is enabled. Moreover do not forget to use log4net compiled in release mode to production code, the above timing with release version of log4net are the followings.

log1.Debug("TEST") = 359.375
if (log1.IsDebugEnabled) log1.Debug("TEST") = 250
if (isDebugEnabled)  log1.Debug("TEST") = 0
log1.Debug("TEST" + I.ToString() + "other") = 2296.875
if (log1.IsDebugEnabled) log1.Debug("TEST" + I.ToString() + "other") = 250
if (isDebugEnabled)  log1.Debug("TEST" + I.ToString() + "other") = 15.625

As you can expect, the release version have really better performance.

Alk.

Tags: Logging log4net

Today I was upgrading a Mantis bug tracking system, to avoid problems I backup the db and tried to restore in a different catalog. The restore procedure fail with the error

MySQL server has gone away

My first question is “gone away? and where? it is gone in vacation?” this is a perfect example of strange error message, fortunately I suspect that the problem was due to a table with BLOB field with great data, and in fact the restore process generated this error during the restore of  a very big row. after some search I found that I can increase the packet size for my server going into the server directory, edit the my.ini file adding this line

set-variable=max_allowed_packet=5M

that increase the maximum packet size to 5 M then everything went ok.

alk.

Tags: MySql

[ServiceContract(SessionMode = SessionMode.Required, CallbackContract = typeof(IL4NClient))]
public interface IL4NServer
{
    [OperationContract]
    Boolean Register();

    [OperationContract]
    Boolean RegisterForSpecificLogger(params String[] loggerNameList);
}

Now I can choose the name of the logger I’m interested to filter messages log.

But this is not the only improvement I need. Quite often it happens that developer X called you telling “When I press the button Y the application responds after 20 seconds”, then you see with the SQL profiler that tons of query gets issued to the database. For a layered and complex application it can be difficult to understand where that queries are issued in the code, so I need a way to get a valid stack trace from the logger. To accomplish this task I modified the LogMessage object

[DataContract]
public class LogMessage
{
    [DataMember]
    public String Message { get; set; }

    [DataMember]
    public List<StackStep>  StackSteps { get; set; }

    public LogMessage()
    {
        StackSteps = new List<StackStep>();
        StackTrace trace = new StackTrace(true);
        var interestingFrames = from StackFrame frame in trace.GetFrames()
                                where frame.GetMethod().DeclaringType.Assembly.GetName().Name != "LiveLogger4Log4Net"
                                      && frame.GetMethod().DeclaringType.Assembly.GetName().Name != "log4net"
                                                && frame.GetFileLineNumber() != 0
                                select new StackStep()
                                           {
                                               SourceFile = frame.GetFileName(),
                                               LineNumber = frame.GetFileLineNumber()
                                           };
        StackSteps.AddRange(interestingFrames);
    }
}

First I have inserted in the message a list of stacksteps, a class that contains filename and line number, in the constructor of the message I use the StackTrace .NET class to obtain the stack trace, then I do a linq query to remove all the steps that have no source file or are part of my logging system. The result is really interesting.

Not only I’m able to intercept NHibernate generated SQL, but I have a full stack trace that tells me where the query is generated, now the next step is to build a better client interface to present the result in a more usable and readable form.

alk.

Tags: log4net NHibernate

When you work with nhibernate you can use show-sql configuration parameter to instruct nhibernate to show generated sql, but how can you see this output in a running windows application? You should know that NHibernate has various log4Net logger, and you can instruct the session to dump all sql code to a logger, here it is a possible configuration

<appender name="WCFAppender" type="LiveLogger4Log4Net.WCFAppender, LiveLogger4Log4Net">
    <layout type="log4net.Layout.PatternLayout" >
        <conversionPattern value="%date [%thread] %-5level %logger %ndc - %message%newline" />
    </layout>
</appender>

<logger name="NHibernate.SQL" additivity="false">
    <level value="DEBUG" />
    <appender-ref ref="WCFAppender" />
</logger>

With this configuration I instruct NHibernate to log to WCFAppender all generated SQL. Now I can attach a log viewer to a running application and look in real time to the sql instruction that nhibernate generates. You can attach more than one application, whenever you want.

Welcome to log4net live logging monitor

alk.

Tags: log4Net NHibernate

The fundamental step to obtain a good logging infrastructure, is to use one of the libraries available in the open source world, and probably you will end using log4net  because it is really good. One of the most important characteristic of a good infrastructure for logging is the ability to change the destination of logs without recompiling, and the possibility to extend the basic logging facility with custom destination storage.

One of the most useful appender is the AdoNet one, that permits you to store logs into database, then you can query them with the full power of SQL, even from a remote machine. This is really good but sometime testers call me telling “hey, when I do this and that the page raise an error” so I need to connect to log database, then look into the log trying to see what’s happened…  this is good but not enough, I need a live logger, a way to attach to a remote process and look at the logs in realtime, in this way I can tell to the tester, please do again all the action that lead to the bug, while I’m watching at all the logging that are generated. log4Net has some network appender, the UDPAppender but I need to connect to a internet machine, and I want the log to travel in the network only when there is attached client.

With this need in mind I proceed to create a Wcf appender for log4net using a publish subscribe technique, here is the two contract interfaces.

[ServiceContract(SessionMode = SessionMode.Required, CallbackContract = typeof(IL4NClient))]
public interface IL4NServer
{
    [OperationContract]
    Boolean Register();
}

[ServiceContract]
public interface IL4NClient
{
    [OperationContract(IsOneWay = true)]
    void ReceiveLog(LogMessage log);

}

For those not familiar with wcf the CallbackContract is a technique for the server to obtain a callback to sent one way messages to clients. Here it is a simple server that uses these two interfaces

public class AppenderService : IL4NServer
{
    #region IL4NServer Members

    private static List<IL4NClient> clients = new List<IL4NClient>();
    bool IL4NServer.Register()
    {
        lock (clients)
            clients.Add(OperationContext.Current.GetCallbackChannel<IL4NClient>());
        return true;
    }

    #endregion

    /// <summary>
    /// Called by the appender, it append a log.
    /// </summary>
    /// <param name="loggingEvent"></param>
    public static void Append(LoggingEvent loggingEvent)
    {
        LogMessage message = new LogMessage() {Message = loggingEvent.MessageObject.ToString()};
        lock (clients)
        {
            for (Int32 I = clients.Count - 1; I >= 0; --I)
            {
                try
                {
                    clients[I].ReceiveLog(message);
                }
                catch (Exception)
                {
                    clients.RemoveAt(I);
                }
            }
        }
    }
}

thanks to the OperationContext.Current.GetCallbackChannel, the server is able to obtain an instance to a proxy that can be used to communicate back to the client through the IL2NClient interface. For each client that calls Register(), the server add the client callback to a inner static list. The Append() static method can be called from everywhere to send a log to all registered clients. As you can see, the code cycle trough all registered clients, and for each clients that generates exception that client is removed from the list.

Now I can create a very simple appender for Log4Net

    public class WCFAppender : AppenderSkeleton
    {
        private ServiceHost host;

        public WCFAppender()
        {
            try
            {
                host = new ServiceHost(typeof(AppenderService));
                host.Open();
            }
            catch (Exception ex)
            {

                throw;
            }
        }

        protected override void Append(LoggingEvent loggingEvent)
        {
            AppenderService.Append(loggingEvent);
        }

        override protected bool RequiresLayout
        {
            get { return true; }
        }

        protected override void OnClose()
        {
            host.Close();
            base.OnClose();
        }

        #endregion Override implementation of AppenderSkeleton

    }

This appender is really simple, it host a communication foundation server for the AppenderService in his constructor and in Append() method it simply called static Append() method of the AppenderService.

With this simple class I can now configure an application to use this custom appender, and then you can connect to it and intercept all the log from another application, creating a live logging listener. Here is a screenshot of a running demo

As you can see I create a simple windows form with a button to generate warn, then I can open a simple console application that connects and listen to all generated logs. You can attach how many listener program as you want.

A complete example can be found here http://nablasoft.googlecode.com/svn/trunk/Log4NetLive.

alk.

Tags: log4Net Appenders:Logging